Various systems have been developed for determining the presence of, or the amount of, various analytes in a sample of interest. In a health care context, many such systems, such as systems involving test strips and test meter devices, are simple enough to be used by a person who is not medically trained. For example, such systems have been developed for a person to test blood cholesterol levels, blood glucose levels, urine analytes indicative of pregnancy, such as human chorionic gonadotropin, and the like, in a home setting. An example of a system for use in determining blood glucose levels is the FreeStyle® blood glucose monitoring system available from TheraSense, Inc. of Alameda, Calif. This electrochemical system is particularly advantageous in that a person need only provide a very small sample of blood to obtain a useful and reliable reading of the concentration of glucose in the blood sample.
While it is useful to determine the concentration of glucose in blood, it is particularly useful to determine the amount of irreversibly glycated hemoglobin, or HbA1c, relative to the amount of total hemoglobin, present in a sample of blood. An example of a method for conducting an electrochemical HbA1c assay is set forth in the above-referenced U.S. Patent Application Publication No. 2002/0172992 of Heller. HbA1c refers to glycated hemoglobin formed by a bond between an amine group of hemoglobin and an aldehyde group of glucose, for example, between the amino group of the N-terminal valine of the β-chain of hemoglobin and the aldehyde group of glucose. The binding reaction first forms a Schiff's base and then a stable ketoamine by Amadori rearrangement. The rate of HbA1c formation is directly proportional to the concentration of glucose in the blood. The percentage of HbA1c (i.e., a ratio of the amount of glycated hemoglobin (HbA1c) to the amount of total hemoglobin (Hb) in the blood, multiplied by 100) has come to be taken as a measure of the level of blood glucose control a diabetic has maintained for a period of two or three months prior to the measurement. As such, percentage HbA1c has become an important result by which health care providers can assist diabetics in their care.
Often, it is the health care provider, such as a physician, for example, that is called upon arrange for an assay of a patient's blood to determine HBA1c percentage. In this context, the physician may recognize a need for an HbA1c measurement concerning a patient, such as a diabetic patient, during an office visit. Typically, the physician asks the patient to go to a laboratory to have a blood sample drawn, whereupon the laboratory tests the sample to obtain an HbA1c measurement and provides the physician with the measurement result hours or days after the office visit. Because of the time lag between the office visit and the physician's receipt of the result, the physician typically reviews the result long after the patient has left the office. If the physician believes that further consultation with the patient is required in light of the test result, the patient must be contacted again. This system is not particularly convenient, expedient, or cost-effective.
Thus, a market demand has developed for a system for use in either the home of a user or patient or the office of a health care provider that can provide an HbA1c assessment quickly and accurately. Typically, a system designed for a person, such as a diabetic, who is not medically trained, to assay a blood sample for HbA1c includes a test strip and a test meter. The test strip and test meter is generally used to determine the amount of irreversibly glycated hemoglobin, HbA1c, relative to the amount of total hemoglobin, Hb, present in a sample of blood. Existing assay systems that can be used to determine an HbA1c value or percentage include the DCA 2000 analyzer of Bayer Diagnostics of Tarrytown, N.Y., the Glycosal test of Provalis Diagnostics Limited of Flintshire, in the United Kingdom, and the A1cNow monitor commercially available from Metrika, Inc. of Sunnyvale, Calif., by way of example.
In recent years, research efforts have focused on creating assays that are both highly accurate and fast. However, existing HbA1c assays typically require a series of steps involving pre-treatment of a blood sample, such as the dilution of a blood sample and/or the lysing of the blood cells in the blood sample, and the subsequent treatment of the sample to separate its various components. In some of these existing HbA1c assays, one or more of the pre-treatment steps must be carried out by the user before he or she can use the test device to assay the blood sample. For example, the above-referenced A1cNow monitor, which is based on technology described in U.S. Pat. No. 5,837,546 of Allen et al., entitled “Electronic Assay Device and Method,” which is incorporated herein in its entirety by this reference, is said to provide an HbA1c test result in eight minutes using a relatively small sample of blood. However, a user of the A1cNow monitor must dilute the blood sample prior to testing the diluted sample using the A1cNow monitor. Further by way of example, it is believed that the above-mentioned Glycosal test requires lysing of the blood sample prior to testing the lysed sample using the Glycosal test. Systems and methods that require such pre-treatment of a sample by a user are generally not convenient or easy for the user and are subject to user error. These systems and methods are thus not ideal for users in self-test situations. Likewise, as these systems and methods require pre-treatment steps on the part of a physician in physician-test situations, they are not particularly convenient or ideal for a physician to use in an office setting. Further development of blood glucose assay devices and systems, and methods of using same, is desirable.